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Bradley, JM, Svistunenko DA, Pullin J, Hill N, Stuart RK, Palenik B, Wilson MT, Hemmings AM, Moore GR, Le Brun NE.  2019.  Reaction of O-2 with a diiron protein generates a mixed-valent Fe2+/Fe3+ center and peroxide. Proceedings of the National Academy of Sciences of the United States of America. 116:2058-2067.   10.1073/pnas.1809913116   AbstractWebsite

The gene encoding the cyanobacterial ferritin SynFtn is up-regulated in response to copper stress. Here, we show that, while SynFtn does not interact directly with copper, it is highly unusual in several ways. First, its catalytic diiron ferroxidase center is unlike those of all other characterized prokaryotic ferritins and instead resembles an animal H-chain ferritin center. Second, as demonstrated by kinetic, spectro-scopic, and high-resolution X-ray crystallographic data, reaction of O-2 with the di-Fe2+ center results in a direct, one-electron oxidation to a mixed-valent Fe2+/Fe3+ form. Iron-O-2 chemistry of this type is currently unknown among the growing family of proteins that bind a diiron site within a four alpha-helical bundle in general and ferritins in particular. The mixed-valent form, which slowly oxidized to the more usual di-Fe3+ form, is an intermediate that is continually generated during mineralization. Peroxide, rather than superoxide, is shown to be the product of O-2 reduction, implying that ferroxidase centers function in pairs via long-range electron transfer through the protein resulting in reduction of O-2 bound at only one of the centers. We show that electron transfer is mediated by the transient formation of a radical on Tyr40, which lies similar to 4 angstrom from the diiron center. As well as demonstrating an expansion of the iron-O-2 chemistry known to occur in nature, these data are also highly relevant to the question of whether all ferritins mineralize iron via a common mechanism, providing unequivocal proof that they do not.

Palenik, B.  2012.  Recent functional genomics studies in marine synechococcus. Functional Genomics and Evolution of Photosynthetic Systems. 33( Burnap VRLWFJ, Ed.).:103-118.   10.1007/978-94-007-1533-2_4   Abstract

Marine Synechoccocus are major contributors to global primary productivity. Genomics and metagenomics have revealed high levels of gene content diversity in these cyanobacteria, partly due to horizontal gene transfer. These differences would be extremely important for ecological niche adaptation. Functional genomics studies using microarrays are now revealing how gene expression in marine cyanobacteria is responding to common environmental stresses such as nutrient deprivation, metal stress, and even the presence of other microbes. Many genes highly expressed under environmental stresses seem to be clade - or even strain-specific, which may change our view of how microbes adapt to new environmental conditions.

Palenik, B, Dyhrman ST.  1998.  Recent progress in understanding the regulation of marine primary productivity by phosphorus. Phosphorus in Plant Biology: Regulating Roles in Molecular, Cellular, Organismic and Ecosystem Processe. ( Lynch JP, Deikman J, Eds.).:26-38., Rockville, MD: American Society of Plant Physiologists Abstract
Paz-Yepes, J, Brahamsha B, Palenik B.  2013.  Role of a Microcin-C-like biosynthetic gene cluster in allelopathic interactions in marine Synechococcus. Proceedings of the National Academy of Sciences of the United States of America. 110:12030-12035.   10.1073/pnas.1306260110   AbstractWebsite

Competition between phytoplankton species for nutrients and light has been studied for many years, but allelopathic interactions between them have been more difficult to characterize. We used liquid and plate assays to determine whether these interactions occur between marine unicellular cyanobacteria of the genus Synechococcus. We have found a clear growth impairment of Synechococcus sp. CC9311 and Synechococcus sp. WH8102 when they are cultured in the presence of Synechococcus sp. CC9605. The genome of CC9605 contains a region showing homology to genes of the Escherichia coli Microcin C (McC) biosynthetic pathway. McC is a ribosome-synthesized peptide that inhibits translation in susceptible strains. We show that the CC9605 McC gene cluster is expressed and that three genes (mccD, mccA, and mccB) are further induced by coculture with CC9311. CC9605 was resistant to McC purified from E. coli, whereas strains CC9311 and WH8102 were sensitive. Cloning the CC9605 McC biosynthetic gene cluster into sensitive CC9311 led this strain to become resistant to both purified E. coli McC and Synechococcus sp. CC9605. A CC9605 mutant lacking mccA1, mccA2, and the N-terminal domain of mccB did not inhibit CC9311 growth, whereas the inhibition of WH8102 was reduced. Our results suggest that an McC-like molecule is involved in the allelopathic interactions with CC9605.